U.S. patent number 5,127,599 [Application Number 07/548,263] was granted by the patent office on 1992-07-07 for deceleration zone in a linear motor in-track transit system.
This patent grant is currently assigned to UTDC, Inc.. Invention is credited to Pierre Veraart.
United States Patent |
5,127,599 |
Veraart |
July 7, 1992 |
Deceleration zone in a linear motor in-track transit system
Abstract
A deceleration zone in a linear motor in-track transit system is
provided. The transit system includes a guideway and at least one
vehicle carrying a linear motor secondary moveable along the
guideway between a freight loading station and a freight unloading
station. Linear induction motor (LIM) primaries are disposed along
the guideway at spaced intervals to provide thrust to the vehicles.
Deceleration zones are designated at certain segments of the
guideway wherein reduced speed of the vehicles is required. The
deceleration zones include a plurality of spaced permanent magnet
decelerators located along the guideway adjacent the vehicle
entrance end of the deceleration zone. The decelerators cause eddy
currents to flow in the linear motor secondaries carried by
vehicles passing thereover due to the magnetic interaction between
the decelerators and the linear motor secondaries. The eddy
currents result in a retarding thrust being supplied to the
vehicles. A synchronous speed linear motor primary is also located
in the deceleration zones adjacent the vehicle exit end thereof and
functions to supply thrust of an appropriate magnitude and
direction to the vehicles to cause vehicles of different mass to
leave the deceleration zone at substantially the same speed.
Inventors: |
Veraart; Pierre (Kingston,
CA) |
Assignee: |
UTDC, Inc. (Kingston,
CA)
|
Family
ID: |
24188072 |
Appl.
No.: |
07/548,263 |
Filed: |
July 5, 1990 |
Current U.S.
Class: |
246/182R;
104/292; 188/164; 246/187B |
Current CPC
Class: |
B60L
15/005 (20130101); Y02T 10/64 (20130101); B60L
2220/12 (20130101); B60L 2200/26 (20130101); Y02T
10/644 (20130101); B60L 2220/14 (20130101); Y02T
10/645 (20130101) |
Current International
Class: |
B60L
15/00 (20060101); B61L 003/06 () |
Field of
Search: |
;188/155,158,159,164,165
;246/182R,182A,182B,182C,187B ;104/292 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
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|
0158114 |
|
Nov 1985 |
|
EP |
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0160523 |
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Nov 1985 |
|
EP |
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278532 |
|
Aug 1988 |
|
EP |
|
2257773 |
|
May 1924 |
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DE2 |
|
0012804 |
|
Jan 1989 |
|
JP |
|
Other References
Patent Abstracts of Japan, vol. 5, No. 163 (E-78) (835), Oct. 20,
1981. .
Patent Abstracts of Japan, vol. 10, No. 105 (M-471) (2162), Apr.
19, 1986. .
Patent Abstracts of Japan, vol. 9, No. 110 (E-314) (1833), May 15,
1985..
|
Primary Examiner: Werner; Frank E.
Assistant Examiner: Lowe; Scott L.
Attorney, Agent or Firm: Drobile; James A. Rosenthal; Robert
E.
Claims
I claim:
1. A deceleration zone in a linear motor in-track transit system,
said transit system including a guideway and at least one vehicle
movable along said guideway, said vehicle including linear motor
secondary means secured thereto, said deceleration zone being
located along a section of said guideway and having a vehicle
entrance end and a vehicle exit end, said deceleration zone
comprising:
magnetic breaking means in the form of at least one permanent
magnet decelerator positioned along said guideway adjacent said
vehicle entrance end; and
linear motor primary means positioned along said guideway adjacent
said vehicle exit end wherein said magnetic braking means operates
independently of said linear motor primary means and interacts with
the linear motor secondary means secured to a vehicle to provide a
substantially constant retarding thrust thereto to slow said
vehicle and wherein said linear motor primary means interacts with
the linear motor secondary means secured to said vehicle and
provides thrust thereto, said thrust being of a magnitude and
direction so that said vehicle exits said deceleration zone having
a velocity substantially equal to a desired velocity.
2. A deceleration zone as defined in claim 1 wherein said magnetic
braking means includes a plurality of spaced permanent magnet
decelerators.
3. A deceleration zone as defined in claim 2 wherein said permanent
magnet decelerators are located at spaced intervals along said
guideway with consecutive decelerators being spaced so that the
center to center spacing therebetween is equal to the length of a
linear motor secondary means secured to a vehicle.
4. A deceleration zone as defined in claim 3 wherein said linear
motor primary means is in the form of a synchronous speed linear
motor primary.
5. A deceleration zone as defined in claim 4 wherein said
synchronous speed linear motor primary is chosen to have a peak
thrust equal to or greater than said constant retarding thrust
developed by said magnetic braking means.
6. A deceleration zone as defined in claim 5 wherein said permanent
magnet decelerators are arranged to decelerate vehicles having a
mass less than a predetermined mass to a speed less than the
synchronous speed of said linear motor primary and to decelerate
vehicles having a mass greater than said predetermined mass to a
speed greater than said synchronous speed, said synchronous speed
linear motor primary accelerating said vehicles travelling below
said synchronous speed and decelerating said vehicles travelling
above said synchronous speed so that said vehicles leave said
deceleration zone at substantially said synchronous speed.
7. A deceleration zone as defined in claim 6 wherein said
predetermined mass is equal to the mass of an average vehicle
carrying an average payload in said transit system.
8. A decelerator for use in an in-track transit system
comprising:
magnetic braking means including a plurality of permanent magnet
decelerators for disposition along a guideway at spaced intervals
such that the center to center spacing therebetween is equal to the
length of a reaction element secured to a vehicle in said transit
system, said magnetic braking means being operable to provide a
substantially constant retarding thrust to a vehicle passed
thereover; and
a synchronous speed linear motor primary for disposition along said
guideway downstream from said magnetic braking means, said
synchronous speed linear motor primary being operable to supply a
thrust to said vehicle having a magnitude and direction so that
said vehicle assumes a velocity substantially equal to the
synchronous speed of said synchronous speed linear motor
primary.
9. A transit system comprising:
a guideway;
at least one vehicle movable along said guideway, said vehicle
having a linear motor secondary secured thereto;
a plurality of linear motor primaries disposed along said guideway
at spaced intervals, said primaries communicating with a linear
motor secondary on a vehicle to supply thrust thereto;
at least one deceleration zone defined by a section of said
guideway and having a vehicle entrance end and a vehicle exit end,
said deceleration zone including magnetic braking means in the form
of at least one permanent magnet decelerator positioned along said
guideway adjacent said vehicle entrance end; and
a linear motor primary positioned along said guideway adjacent said
vehicle exit end wherein said magnetic braking means operates
independently of said linear motor primary and interacts with the
linear motor secondary means secured to a vehicle to provide a
substantially constant retarding thrust thereto to slow said
vehicle and wherein said linear motor primary interacts with the
linear motor secondary secured to said vehicle and provides thrust
thereto, said thrust being of a magnitude and direction so that
said vehicle exists and deceleration zone having a velocity
substantially equal to a desired velocity.
10. A transit system as defined in claim 9 wherein said magnetic
braking means includes a plurality of spaced permanent magnet
decelerators.
11. A transit system as defined in claim 10 wherein said permanent
magnet decelerators are located at spaced intervals along said
guideway with consecutive decelerators being spaced so that the
center to center spacing therebetween is equal to the length of a
linear motor secondary means secured to a vehicle.
12. A transit system as defined in claim 11 wherein said linear
motor primary means is in the form of a synchronous speed linear
motor primary.
13. A transit system as defined in claim 12 wherein deceleration
zones are positioned along said guideway adjacent vehicle entrance
ends of curved segments of said guideway, track switches and
downgrades in said guideway.
Description
FIELD OF THE INVENTION
The present invention relates to a transit system and in particular
to a deceleration zone in a linear motor in-track transit
system.
BACKGROUND OF THE INVENTION
Transit systems are well known in the art. Some conventional
transit systems implement linear induction motors (LIM's) wherein
the LIM primaries are located at spaced intervals between the rails
of a track and wherein the LIM secondaries or reaction rails are
secured to the chassis of vehicles travelling along the track.
These transit systems are conventionally designated as LIM in-track
transit systems. In these in-track transit systems and as in all
transit systems, when more than one vehicles are travelling along
the track, it is important to avoid collisions between vehicles.
This of course requires the speed of all vehicles travelling along
the track to be accurately controlled to ensure that vehicle
spacing is maintained. In many systems, to increase vehicle
throughput, the vehicles are propelled at high speeds. However,
typically in certain segments of the track such as curves, track
switches, etc., high speeds are not permitted due to the
possibility of derailment. Accordingly, deceleration zones are
provided adjacent these sections of track to slow the vehicles so
that they travel through these sections of track at a safe
speed.
In conventional systems, closed loop control has been implemented
in the deceleration zones using multiple LIM primaries and
associated controllers therefor. Although these components provide
excellent vehicle control, a problem exists in that if the linear
induction motor primaries and/or controllers fail, vehicles are not
slowed at all (except due to friction and drag) in the deceleration
zone and thus, may enter the following sections of the track at
unsafe speeds. Furthermore, another problem exists in that the
controllers and LIM primaries are expensive and thus, conventional
systems using multiple LIM primaries increase construction and
operation costs of the transit system.
A prior art in-track transit system is shown in U.S. Pat. No.
4,716,346 to Matsuo which discloses a conveying apparatus including
a track having a curve and a carriage movable along the track. The
track is provided with a plurality of LIM stators disposed along
the straight portions of the track. A reaction rail is secured to
the chassis of the carriage and communicates with the stators.
Carriage detection sections are also located on the track and are
positioned before and after the curved segment of the track. The
carriage detection sections co-operate with the LIM stators and
detect the speed and mass of the carriage. When a moving carriage
passes over a carriage detection section, the speed of the carriage
is calculated. A predetermined reverse thrust is then provided to
the carriage via an energizing LIM stator and the speed of the
carriage is once again calculated. This allows the mass of the
carriage to be determined so that the maximum speed of the carriage
over the curved section of track can be determined. Once the
maximum speed has been calculated, it is compared with the speed of
the carriage so that the necessary thrust can be applied to the
carriage to ensure that the vehicle travels at the correct maximum
speed over the curved segment of track.
As can be seen, the carriage detection sections in the Matsuo
system require two controllers and two LIM stators to permit the
mass of the carriage to be calculated so that the second LIM stator
is capable of being operated to supply the necessary thrust to the
carriage, thereby ensuring the carriage to travel along the curved
section of the track at the desired speed. It should be apparent
that if the controllers or LIM stators in the Matsuo system fail,
the carriage is not slowed prior to entering the curved section of
the track. Furthermore, the cost of the multiple controllers and
LIM stators makes this type of velocity control zone expensive.
It is therefore an object of the present invention to obviate or
mitigate the above disadvantages by providing a novel deceleration
zone in a linear motor in-track transit system.
SUMMARY OF THE INVENTION
According to the present invention there is provided a deceleration
zone in a linear motor in-track transit system, said transit system
including a guideway and at least one vehicle movable along said
guideway, said vehicle including linear motor secondary means
secured thereto, said deceleration zone being located along a
section of said guideway and having a vehicle entrance end and a
vehicle exit end, said deceleration zone comprising:
magnetic braking means positioned along said guideway adjacent said
vehicle entrance end; and
linear motor primary means positioned along said guideway adjacent
said vehicle exit end wherein said magnetic braking means operates
independently of said linear motor primary means and interacts with
the linear motor secondary means secured to a vehicle to provide a
substantially constant retarding thrust thereto to slow said
vehicle and wherein said linear motor primary means interacts with
the linear motor secondary means secured to said vehicle and
provides thrust thereto, said thrust being of a magnitude and
direction so that said vehicle exits said deceleration zone having
a velocity substantially equal to a desired velocity.
Preferably, the magnetic braking means includes at least one
permanent magnet decelerator (PMD) and the deceleration zone is
positioned in the transit system so that vehicles entering the
deceleration zone have a speed in the constant force range of the
permanent magnet decelerator. It is also preferred that the linear
motor primary is in the form of a synchronous linear induction
motor. Preferably the permanent magnet decelerators are arranged to
slow vehicles of a high mass to a velocity above the synchronous
speed of the LIM primary and to slow vehicles of lower mass to a
velocity less than the synchronous speed of the linear induction
motor primary.
In another aspect of the present invention, there is provided a
decelerator for use in an in-track transit system comprising:
magnetic braking means for disposition along a guideway and
operable to provide a substantially constant retarding thrust to a
vehicle having a reaction element secured thereto and passing
thereover; and
a synchronous linear motor primary for disposition along said
guideway downstream from said magnetic braking means, said
synchronous linear motor primary being operable to supply a thrust
to said vehicle having a magnitude and direction so that said
vehicle assumes a velocity substantially equal to the synchronous
speed of said synchronous linear motor primary.
In still yet another aspect of the present invention there is
provided a transit system comprising:
a guideway;
at least one vehicle movable along said guideway, said vehicle
having a linear motor secondary secured thereto;
a plurality of linear motor primaries disposed along said guideway
at spaced intervals, said primaries communicating with a linear
motor secondary on a vehicle to supply thrust thereto; and
at least one deceleration zone located along a section of said
guideway and having a vehicle entrance end and a vehicle exit end,
said deceleration zone including magnetic braking means positioned
along said guideway adjacent said vehicle entrance end; and
a linear motor primary positioned along said guideway adjacent said
vehicle exit end wherein said magnetic braking means operates
independently of said linear motor primary and interacts with the
linear motor secondary secured to a vehicle to provide a
substantially constant retarding thrust thereto to slow said
vehicle and wherein said linear motor primary interacts with the
linear motor secondary secured to said vehicle and provides thrust
thereto, said thrust being of a magnitude and direction so that
said vehicle exits said deceleration zone having a velocity
substantially equal to a desired velocity.
Preferably, the deceleration zones are located in the transit
system adjacent and upstream track switches, curves and downgrades
to slow vehicles before they enter these sections of the track.
The present invention provides advantages in that the time taken
for vehicles having different mass passing through the deceleration
zone remains substantially constant thereby maintaining vehicle
separation. This allows the throughput of vehicles in the transit
system to be increased as compared with conventional systems.
Moreover, other advantages exist in that even if the linear motor
primary or controller therefor fails, the permanent magnet
decelerators provide a retarding thrust to the vehicles ensuring
that the vehicles are slowed prior to entering the following
section of track. Also, since a synchronous linear motor primary is
used, a complex controller for the motor is not required thereby
reducing costs.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the present invention will now be described by way
of example only with reference to the accompanying drawings in
which:
FIG. 1 is a top plan view of a transit system;
FIG. 2 is a side view of a deceleration zone in the transit system
shown in FIG. 1;
FIG. 3 shows graphs illustrating characteristics of permanent
magnet decelerators used in the deceleration zone shown in FIG.
2;
FIG. 4 shows a graph illustrating the response of vehicles passing
over the permanent magnet decelerators shown in FIG. 2;
FIG. 5 shows a response curve of a synchronous linear induction
motor used in the deceleration zone shown in FIG. 2; and
FIG. 6 shows response curves of vehicles passing through the
deceleration zone shown in FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIGS. 1 and 2, a transit system is shown and
generally indicated by reference numeral 10. The transit system 10
includes a track 12 having a pair of rails 14,16. Linear induction
motor (LIM) primaries 18 are located between the rails of the track
12 at spaced intervals. Freight-carrying vehicles 20 are supported
by the track 12 and are movable therealong. Each vehicle 20
includes a reaction rail 22 or LIM secondary secured to its chassis
which cooperates with the linear induction motor primaries 18 in a
known manner to propel the vehicles 20. Since the operation of
linear induction motors is well known to those of skill in the art,
a detailed description thereof will not be discussed herein.
As can be seen, the track 12 extends between a manual freight
loading station 28 and an automatic freight unloading station 30.
The majority of the track 12 extending between the two stations 28,
30 is generally horizontal and straight. These sections of the
track are designated by reference numerals 36 and 38 and are
sections of the track where vehicles are propelled at high speeds
to increase vehicle throughput. However, the track also experiences
a downgrade 32 (best seen in FIG. 2) and a curve 34 (best seen in
FIG. 1) along a portion of its length. Deceleration zones D.sub.1
and D.sub.2 are also designated along portions of the track 12
adjacent the vehicle entrance end of the downgrade 32 and the
vehicle entrance end of the curve 34 respectively. The deceleration
zones D.sub.1 and D.sub.2 are identical and function to slow
vehicles 20 travelling along the track between the stations 28,30
to a desired speed before the vehicles leave the deceleration zones
and enter the following sections of track as will be described in
more detail herein.
A merging section of track 40 intersects the main track 12 at a
location adjacent the bottom of the downgrade 32. Similarly, the
merging section of track 40 has linear induction motor primaries 18
disposed between the rails thereof at spaced intervals to propel
vehicles 20.
Vehicle stopping zones S.sub.1 and S.sub.3 are designated along the
track 12 in the loading and unloading stations 28,30 respectively
and function to stop the vehicles 20 at the stations so that
freight can be placed on the vehicles and removed therefrom. A
stopping zone S.sub.2 is also designated along a section of the
merge track 40 so that vehicles travelling therealong are
automatically stopped before entering the main track 12. The
stopping zones S.sub.1, S.sub.2 and S.sub.3 include a primary brake
and a secondary brake, each brake of which is operable to stop the
vehicle. However, the secondary brake remains in an inoperative
condition unless the vehicle 20 has been detected as passing a
designated stopping point in the stopping zone due to failure or
malfunction of the primary brake.
To increase throughput in the transit system 10, it is desired to
move the vehicles 20 along the track 12 between the loading and
unloading stations 28,30 respectively as fast as possible with
accurate control to avoid high speed collisions. This collision
avoidance is achieved by dividing the track into fixed segments or
blocks B.sub.1 to B.sub.12. When a vehicle 20 is detected as being
present in a block B.sub.z by sensors positioned along the track, a
block occupied signal BLO 35 is generated by a controller 44 in the
block B.sub.z and is applied to the controller 44 in the previous
block B.sub.x-1. If a vehicle enters the previous block B.sub.x-1
while the controller 44 therein is receiving the block occupied
signal BLO from the adjacent upstream block B.sub.x, the LIM
primaries 18 in the block B.sub.x-1 are operated by the controller
44 in a manner to cause the vehicle 20 to be stopped within the
block B.sub.x-1. This prevents two vehicles from being located
within the same block and thus, avoids collisions between vehicles
and maintains vehicle spacing. This operation is achieved by
ensuring that the length of each block B.sub.x is sufficient to
stop a vehicle completely or at least to slow a vehicle to a speed
such that even if the vehicles collide in the block B.sub.x, the
impact resulting from the collision can be withstood by the
vehicles without any resulting damage.
FIG. 2 better illustrates the deceleration zone D.sub.1 positioned
upstream from the downgrade 32. Since the deceleration zones
D.sub.1 and D.sub.2 are identical, only the deceleration zone
D.sub.1 will be described in detail herein. As can be seen, the
deceleration zone D.sub.1 is located within one of the blocks
B.sub.4 and is divided into two sections, namely a passive section
50 located adjacent the vehicle entrance end of the deceleration
zone D.sub.1 and an active section 52 located adjacent the vehicle
exit end of the deceleration zone. The passive section 50 includes
a plurality of permanent magnets decelerators (PMD's) 54 such as
those manufactured by Northern Magnetics Inc. The PMD's 54 are
located between the rails 14,16 of the track 12 at spaced
intervals. The active section 52 includes a synchronous speed
linear induction motor primary 56, such as for example a fixed
frequency asynchronous linear induction motor primary. The PMD's 54
in conjunction with the synchronous LIM primary 56 function to
reduce the speed of vehicles 20 as they pass through the
deceleration zone D while ensuring that vehicles carrying payloads
of different mass pass through the deceleration zone in
substantially the same amount of time and enter the following
section of track 12 at substantially the same speed. The operation
of the deceleration zone in this manner, maintains vehicle spacing
thereby reducing the probability of vehicular collisions. This, of
course, also allows vehicle throughput in the transit system to be
maximized. In addition, since the deceleration zone functions to
slow vehicles to a predetermined speed, the probability of vehicle
derailment in the following sections of track is greatly
reduced.
The arrangement of the PMD's 54 within the deceleration zone D and
the selection of the synchronous speed linear motor primary 56 can
be made to optimize the deceleration zones in terms of the maximum
allowable exit speed and minimum speed of a vehicle in the zone as
well as travel time differentials between vehicles of different
mass passing through the deceleration zone. Although optimization
is often desired, in actual practice, the synchronous speed linear
motor primary is typically selected based on devices available and
used in other segments of the transit system which although do not
result in an optimized deceleration zone, will provide an
acceptable level of performance.
Referring now to FIG. 3, the thrust vs speed characteristics of two
types of PMD's 54 are shown, namely "D" type and "G" type permanent
magnet decelerators. As can be seen, both "D" or "G" type
decelerators provide a somewhat constant braking force to vehicles
20 travelling thereover in the speed range of 4 m/s to 10 m/s
although the magnitudes of the braking forces are different. The
constant braking force applied to the vehicles in this speed range
results in the deceleration of the vehicles becoming primarily a
function of their mass and to a far lesser extent drag. Thus,
vehicles of different mass passing over these decelerators will be
decelerated differently.
This condition is illustrated in FIG. 4 which shows response curves
60,62 for a 250 kg and a 400 kg vehicle respectively travelling
along the track 12 and passing over the passive section 50 of the
deceleration zone D.sub.1. As can be seen, the passive section 50
includes five "D" type PMD's 54 spaced along the track. The spacing
between consecutive PMD's is chosen so that the center to center
spacing of consecutive PMD's is equal to the length L.sub.RP, of
the reaction rail 22 secured to the vehicles 20.
In this instance, both vehicles entered the passive section 50 of
the deceleration zone D.sub.1 having a velocity of 8 m/s. The 400
kg vehicle took approximately two (2) seconds to pass over the
passive section 50 and was slowed to an exit velocity of
approximately 5 m/s. In contrast, the 250 kg vehicle took
approximately four-and-one-half (4.5) seconds to pass over the
passive section 50 and was slowed to an exit velocity of
approximately 1 m/s. In transit systems where high vehicle
throughput is required, the above difference in time taken for
vehicles of different mass to travel thereover is unsatisfactory.
This is due to the fact that the time difference delta T must be
compensated for by increasing vehicle spacing to avoid collisions
which of course decreases vehicle throughput. Thus, these types of
decelerators are unacceptable when used on their own.
To compensate for the operational nature of the PMD's 54, the
synchronous speed linear induction motor (LIM) primary 56 is also
provided in the deceleration zone D. As is well known to those of
skill in the art, the synchronous speed LIM primary 56 operates to
supply thrust having a polarity and direction to a vehicle so that
the vehicle leaves the control zone of the synchronous speed LIM
primary at substantially the synchronous speed of the LIM primary.
FIG. 5 illustrates the characteristics of a synchronous speed LIM
primary having a synchronous speed of approximately 5.7 m/s. As can
be seen, the synchronous speed LIM primary 56 applies a retarding
thrust to vehicles 20 travelling above the synchronous speed and a
propulsive thrust to vehicles travelling below the synchronous
speed. In the present system, the synchronous speed LIM primary 56
is chosen to have a synchronous speed close to that of the desired
exit speed of the vehicles from the deceleration zone D and to have
a peak thrust approximately equal to the retarding thrust of the
PMD's 54.
Although in the present system 10, the synchronous speed linear
motor primary was chosen to have a peak thrust substantially equal
to the thrust of the PMD's 54, it should be apparent that
synchronous speed linear motors having different thrust
characteristics may be employed In general given a specific
arrangement of PMD's 54, a synchronous speed linear motor having a
greater
peak thrust than the PMD's will result in improved performance,
namely, decreasing speed and lower time differentials between
vehicles of different mass passing through the deceleration
zones.
The operation of the transit system 10 and, in particular, the
deceleration zones will be now be described. After a vehicle 20 has
been loaded at the loading station 28, the LIM primaries in each of
the blocks B.sub.x are energized in succession by their controllers
so that the vehicle 20 travels towards the unloading station 30 at
the desired speed. When the vehicle 20 enters block B.sub.3
upstream from the deceleration zone D.sub.1, the vehicle 20 is
propelled by the LIM primaries 18 therein so that the vehicle
enters the deceleration zone D.sub.1 having a speed in the constant
force range of the PMD's 54 and at a speed so that the reverse
thrust applied to the vehicle 20 by the PMD's 54 is insufficient to
stop the vehicle 20. When the vehicle enters the deceleration zone
D.sub.1, the magnetic interaction between the PMD's 54 and the
reaction rail 22 secured to the vehicle 20 causes eddy currents to
flow in the reaction rail 22. This results in a reverse thrust
being applied to the vehicle 20 thereby slowing the vehicle before
the vehicle enters the active section 52 of the deceleration zone
D.sub.1.
To reduce the difference in the time taken for vehicles of
different mass to pass through the deceleration zone D.sub.1, the
number and type of PMD devices 54 used in the passive section 50
are chosen so that a vehicle of average mass in the transit system
10 will leave the passive section 50 having a speed substantially
equal to the synchronous speed of the LIM primary 56. Vehicles of
lower mass than the average will leave the passive section 50 at a
speed less than the synchronous speed while vehicles of greater
mass than the average will leave the passive section 50 at a speed
greater than the synchronous speed.
When the vehicles enter the active section 52, the synchronous
speed LIM primary 56 functions to accelerate the vehicles of lower
mass and decelerate the vehicles of higher mass while allowing the
averaged mass vehicles travelling at the synchronous speed to pass
so that each of the three types of vehicles leaves the deceleration
zone D.sub.1 at substantially the same speed, this speed being
substantially equal to the synchronous speed of the LIM primary 56.
In addition, since the synchronous speed LIM primary 56 decelerates
heavier vehicles and accelerates lighter vehicles, heavier vehicles
take longer to pass over the active section 52 than do lighter
vehicles. This difference in time taken for the heavier vehicles to
pass over the active section 52 somewhat offsets the difference in
time taken for the different massed vehicles to pass over passive
section 50, thereby reducing the overall difference in the time
taken for vehicles of different mass to pass through the
deceleration zone D.sub.1.
This operation is illustrated in FIG. 6 which shows response curves
for a 400 kg vehicle and a 250 kg vehicle passing through the
present deceleration zone D.sub.1. As can be seen, both vehicles
entered the deceleration zone D.sub.1 having a velocity of 8 m/s.
The 400 kg vehicle took two (2) seconds to pass through the
deceleration zone D.sub.1 and had an exit velocity of approximately
5.7 m/s. The 250 kg vehicle took two-and-a-half (2.5) seconds to
pass through the deceleration zone D.sub.1 and had an exit velocity
of approximately 4.5 m/s. Accordingly, the difference in time taken
for the two substantially different mass vehicles to pass through
the deceleration zone was only 0.5 seconds. The difference in the
exit velocity between the two vehicles was approximately 1.25
m/s.
In comparing the above-described vehicular travel through the
deceleration zone D with vehicular travel over only PMD's 54 as
shown in FIG. 4, it can be seen that the difference in exit
velocity of the two different mass vehicles was reduced from 4.9
m/s to 1.25 m/s. Furthermore, the travel time for the vehicles to
pass over these zones was reduced from 2.5 seconds to 0.5 seconds.
If a synchronous linear motor primary having a higher peak thrust
is chosen for use in the deceleration zone, the time and speed
differentials can be further reduced.
Thus, as a vehicle enters the deceleration zone D.sub.1, it is
slowed to a desired speed before travelling along the downgrade 32.
Once the vehicle leaves the downgrade, it is propelled by the LIM
primaries 18 towards the curve 34. The deceleration zone D.sub.2
which is positioned just upstream from the curve 34, functions in
the same manner described above to slow the vehicle before it
enters the curve. After the vehicle 20 has been slowed in the
deceleration zone D.sub.2 and navigates the curve, it is propelled
to the unloading station 30 and stopped so that the freight carried
by the vehicle 20 can be removed.
The present deceleration zone provides advantages in that the use
of the PMD devices in conjunction with the synchronous speed LIM
primary provides an inexpensive decelerator which permits vehicles
of different mass to be slowed in the deceleration zone to
substantially the same exit speed and to travel through the
deceleration zone in substantially the same amount of time.
Moreover, the use of the PMD devices to provide the initial
retarding thrust ensures that all vehicles are slowed even if the
synchronous speed LIM primary fails or in the event of a general
power failure.
Although, the present device shows the use of permanent magnet
devices to slow the vehicle in the passive section, it should be
realized that electromagnet devices can also be used, with the
electromagnets being supplied by a power supply independent of the
synchronous speed LIM primary.
It should be apparent to one of skill in the art that the various
modifications and variations can be made to the present invention
without departing from the scope thereof as defined by the appended
claims.
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